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Summary
Throughout the growing season we measured potato leafhopper infestations, yield and forage quality, and development of glandular hairs. High numbers of nymphs were found on all varieties; however, by 31 July, fewer nymphs were present on most glandular-haired varieties compared to the non-glandular check. No significant differences in yield occurred. Crude protein differences may reflect differences in resistance to PLH feeding damage. Growers should be aware that these glandular-haired alfalfa varieties were, at least in the first year, susceptible to PLH damage. IPM scouting procedures and thresholds for PLH should still be used.

Statistical Analyses: ANOVA and LSD were used to analyze differences among treatments in PLH sweep net counts after [x + 0.5]1/2 transformation, yield, and CP.

Results and Discussion
Potato leafhopper populations: 1997 was a year of extremely high PLH activity. Sweep net counts exceeded the economic threshold in all plots on 16 June and 31 July, and all plots were sprayed on 19 June and 31 July.
Adult counts on 18 July showed no significant differences between the check and 4 of the 5 glandular-haired varieties (Table 1). On 31 July significantly higher numbers (P < or = 0.05) of nymphs occurred in the check compared to 4 of the 5 glandular-haired varieties. This indicates that adults laid fewer eggs or fewer nymphs survived on the glandular-haired varieties.

Yield: In 1997, three cuttings were made (Table 2). There were no significant differences in yield for any single cutting or for total yield, although numerically the check out-yielded all glandular-haired varieties.
Table 2. Alfalfa dry matter yield, PLH resistant alfalfa trial, Orange Co., Va., 1997.

Variety

Dry matter yield (ton/a) 1

Cutting 18 July

Cutting 218 Aug.

Cutting 324 Oct.

Total

Arrest

0.46

0.69

0.32

1.48

Cleansweep

0.47

0.75

0.31

1.54

Dekalb DK 121 HG

0.47

0.71

0.34

1.51

Interceptor

0.48

0.82

0.40

1.70

Pioneer 5347LH

0.53

0.72

0.35

1.59

Check (P 5454)

0.56

0.77

0.40

1.73

1 No significant differences were detected for any single cutting or for total yield (P > 0.05; LSD).

Forage quality: Treatment (variety) source of variation for crude protein (CP) was significant (P < or = 0.05) for the first and second cuttings (Table 3). These cuttings occurred during high PLH activity, and the lower CP percentage in the check compared to some glandular varieties may reflect higher PLH damage.

1 Means within a column followed by the same letter were not significantly different (P > 0.05; LSD).

Glandular hair development: Only 30-40% of the plants in these varieties express the glandular-hair trait. On plants that express the trait, we counted up to 37 and 58 glandular hairs per mm on abaxial leaflet veins and petioles, respectively, and up to 32 glandular hairs per mm2 on stems.